Replacing SkTDArray with SkAutoSTArray to reduce memory allocation overhead in SkTileGrid::search

src/core/SkTileGrid.h

Index: src/core/SkTileGrid.h
diff --git a/src/core/SkTileGrid.h b/src/core/SkTileGrid.h
index e272673c638f255d320e676c0e4fdfd60bb2f511..77d972850fe7bb70fb14ca657bb92c3842e72968 100644
--- a/src/core/SkTileGrid.h
+++ b/src/core/SkTileGrid.h
@@ -25,7 +25,15 @@
  */
 class SkTileGrid : public SkBBoxHierarchy {
 public:
-    typedef void* (*SkTileGridNextDatumFunctionPtr)(SkTDArray<void*>** tileData, SkTDArray<int>& tileIndices);
+    enum {
+        // Number of tiles for which data is allocated on the stack in
+        // SkTileGrid::search. If malloc becomes a bottleneck, we may consider
+        // increasing this number. Typical large web page, say 2k x 16k, would
+        // require 512 tiles of size 256 x 256 pixels.
+        kStackAllocationTileCount = 1024
+    };
+
+    typedef void* (*SkTileGridNextDatumFunctionPtr)(SkTDArray<void*>** tileData, SkAutoSTArray<kStackAllocationTileCount, int>& tileIndices);
 
     SkTileGrid(int xTileCount, int yTileCount, const SkTileGridPicture::TileGridInfo& info,
         SkTileGridNextDatumFunctionPtr nextDatumFunction);
@@ -91,7 +99,7 @@ private:
  *     such that 'a < b' is true if 'a' was inserted into the tile grid before 'b'.
  */
 template <typename T>
-void* SkTileGridNextDatum(SkTDArray<void*>** tileData, SkTDArray<int>& tileIndices) {
+void* SkTileGridNextDatum(SkTDArray<void*>** tileData, SkAutoSTArray<SkTileGrid::kStackAllocationTileCount, int>& tileIndices) {
     T* minVal = NULL;
     int tileCount = tileIndices.count();
     int minIndex = tileCount;